1. Field of the Invention
The present invention relates to a stencil printing machine which creates a printed sheet by forming a perforated image on a stencil sheet based on image data and transferring ink to a print medium through this perforated image on the stencil sheet. Specifically, the present invention relates to a technology for shortening a first print time to form the perforated image and output a first trial print.
2. Description of the Related Art
A conventional stencil printing machine is described in Japanese Patent Laid-Open publication No. Hei 9(1997)-11600. FIG. 1 is a schematic drawing showing main parts of the stencil printing machine described in the publication, the parts being related to stencil making and loading. In FIG. 1, a rolled stencil sheet 2, a writing head 8, a platen roller 7, a pair of first conveyer rollers 12a and 12b, a storage box 13, a pair of second conveyer rollers 14a and 14b, a stencil sheet cutter 10, a stencil positioning sensor 17, a printing drum 4, and a stencil sheet clamp section 4a are arranged along a conveyance route R1. The drawing shows a case where the stencil sheet clamp section 4a is placed at a clamp rotational position where the stencil sheet 2 is clamped, and the writing head 8 is placed at a standby position.
In FIG. 1, the leading edge of the stencil sheet 2 cut with the stencil sheet cutter 10 in the last stencil loading operation is conveyed downstream along the conveying route R1 by the platen roller 7 which is rotated by a platen motor (not shown). At this time, by a head shift driver (not shown), the writing head 8 is located at a pressure contact position where the writing head 8 is in pressure contact with the platen roller 7.
When the stencil positioning sensor 17 detects the leading edge of the stencil sheet 2, a timer (not shown) starts clocking. After a predetermined time period, the platen roller 7 stops rotation, and the leading edge of the stencil sheet 2 stops at a predetermined position (a waiting position) on the conveying route R1. The writing head 8 is then shifted to the standby position, and the leading edge of the stencil sheet 2 stays at the waiting position until the next stencil loading operation starts.
The stencil making and loading operations of the conventional stencil printing machine have been performed according to a procedure as described below.
The stencil making operation is performed in the following manner. The writing head 8 is located at the pressure contact position, and the stencil sheet 2 is subjected to writing (thermal perforation) according to binarized data for stencil making while the stencil sheet 2 sandwiched between the writing head 8 and the platen roller 7 is being conveyed. At this time, the rotation of the second conveyer rollers. 14a and 14b is stopped, the perforated stencil sheet 2 stays between the first conveyer rollers 12a and 12b and the second conveyer rollers 14a and 14b, and is gradually stored in the storage box 13.
A stencil making time period for the stencil sheet 2 which corresponds to a conveying distance L1 between the waiting position of the leading edge of the stencil sheet 2 and the stencil sheet clamp section 4a along the conveying route R1 is measured by a timer or the like as a driving time period of the platen motor 20. When the stencil making time period elapsed after the stencil making is started, the second conveyer rollers 14a and 14b are rotated, and the leading edge of the stencil sheet 2 is conveyed to the stencil sheet clamp section 4a. The rotation of the second conveyer rollers 14a and 14b is then stopped.
When the rotation of the second conveyer rollers 14a and 14b is stopped, the perforated stencil sheet 2 is gradually stored in the storage box 13 again. Meanwhile, a writing operation for the stencil sheet 2 by the platen roller 7 and the writing head 8 is continued while the stencil sheet 2 is being conveyed by the second conveyer rollers 14a and 14b. 
When the writing operation is completed, the writing head 8 is shifted by the head shift driver (not shown) from the pressure contact position to the standby position away from the platen roller 7 by a predetermined distance. This shifting operation of the writing head 8 is called a stencil making pressure release, and the time period required for release of stencil making pressure is defined as a stencil making pressure release time period T.
After the stencil making pressure is released, the printing drum 4 is driven to an angle which is equivalent to a stencil loading length {L−(L1+L2)} from the clamp rotational position by a rotor (not shown), and the stencil sheet 2 is loaded on the printing drum 4. Thereafter, the rotation of the printing drum 4 is once stopped, and the stencil sheet 2 is cut with the stencil sheet cutter 10. A time period required for the cutting is defined as a cutting time period Tk. Herein, L1 is the stencil loading length of the printing drum 4 and L2 is a conveying distance from the stencil sheet cutter 10 to the waiting position of the leading edge of the stencil sheet 2 along the conveying route R1.
Subsequently, the printing drum 4 is rotated again, and part of the stencil sheet 2 with a length of (L1+L2) remaining on the conveying route R1 is loaded thereon. When the stencil sheet clamp section 4a returns to the clamp rotational position, the rotation of the printing drum 4 is stopped. If the stencil positioning sensor 17 does not detect the stencil sheet 2, the stencil loading operation is completed. The writing head 8 is then shifted to the pressure contact position, and the platen roller 7 is rotated. The leading edge of the cut stencil sheet 2 is thus conveyed downstream on the conveying route R1. When the stencil positioning sensor 17 detects the leading edge of the stencil sheet 2, the timer (not shown) starts clocking. The drive of the platen motor 20 is stopped after the predetermined time period, and the rotation of the platen roller 7 is stopped. The leading edge of the stencil sheet 2 stops at the predetermined position (the waiting position) on the conveying route R1.
FIG. 6A shows a time chart related to the aforementioned stencil making (writing), stencil making pressure release, conveying (rotation of platen roller) stencil loading (rotation of printing drum), cutting, and printing/printed sheet discharged operations.
A stencil making operation time period Ts is expressed as Ts=(L−L3)/Sp. Herein, Sp is a peripheral speed of the platen roller 7. Note that L3 is a length (hereinafter, referred to as a margin length) of the stencil sheet 2 corresponding to a margin of the trailing end in the sheet conveying direction in which writing (printing) is not allowed.
The time period required for the stencil making pressure release operation is the stencil making pressure release time period T.
A stencil loading operation time period Tc is the total of a stencil loading time period for loading the stencil sheet 2 with a length of L and the cutting time period Tk of the stencil sheet 2, and is expressed as Tc=L/Sh+Tk. During the stencil sheet loading operation, the printing drum 4 is rotated to load part of the stencil sheet 2 with a length of {L−(L1+L2)} thereon at first. After the cutting time period Tk during which the rotation is being stopped, the printing drum 4 is rotated again to load part of the stencil sheet 2 with a length of (L1+L2) thereon.
Specifically, the length {L−(L1+L2)} of the stencil sheet 2 is expressed as {L−(L1+L2+L3)}+L3}, where L3 is the length of part of the stencil sheet 2 conveyed by the printing drum 4 which is rotated after the stencil making pressure release, and (L1+L2) is the length of the part of the stencil sheet 2 remaining on the conveying route R1 when the stencil sheet 2 is cut with the stencil sheet cutter 10. Herein, Sh is a peripheral speed of the printing drum 4 during the stencil loading.
As for the cutting time period Tk, an example of a shuttle cutter, which cuts the stencil sheet 2 while the stencil sheet 2 is being stopped, is shown according to a later described embodiment. However, the cutting time period Tk can be made to be 0 by using a rotary cutter.
Accordingly, the stencil loading operation time period Tc is expressed as Tc=L/Sh+Tk {L−(L1+L2+L3)+L3}/Sh+Tk+(L1+L2)/Sh.
Consequently, a first print time Tf1 is expressed as Tf1=Ts+T+Tc+Tp, where Tp is a time period for the printing/printed sheet discharged operation.
As described above, in the conventional stencil printing machine, there has been a disadvantage that the first print time is long because of serial processing of the stencil making, stencil making pressure release, stencil loading, cutting, and printing/printed sheet discharged operations.